Carbon dioxide-resistant portland based cement composition

ABSTRACT

The invention provides a carbon dioxide-resistant hydraulic cement composition. The inventive composition comprises a Portland cement, Class C fly ash and water. The Class C fly ash is present in the composition in an amount in the range of from about 5% to less than about 30% by weight based on the total weight of the cementitious components in the composition. In another aspect, the invention provides a method of cementing in a carbon dioxide environment. In yet another aspect, the invention provides a method of enhancing the recovery of a hydrocarbon fluid from a subterranean formation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. Non-Provisional applicationSer. No. 13/223,081 filed on Aug. 31, 2011, now allowed, and which ishereby incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Hydraulic cement compositions are often used in applications that are orwill be associated with a relatively high level of carbon dioxide. Forexample, hydraulic cement compositions are used to encase the well boresof injection and production wells used in connection with enhanced oilrecovery techniques. A fluid commonly used to flood the formation insuch techniques is carbon dioxide. Specifically, the carbon dioxide isinjected into the formation together with water through one or moreinjection wells to drive hydrocarbons in the formation toward one ormore production wells. This technique has proved to be effective inincreasing production of the hydrocarbons from the formation.

Hydraulic cement compositions are also used in other applications thatinvolve or may involve a carbon dioxide environment. Examples includeformation sealing applications and other cementing applicationsassociated with oil, gas, water and geothermal wells and carbon capsulestorage applications associated with power plants.

A problem that can result from the use of hydraulic cement compositionsin applications that are or will be associated with a carbon dioxideenvironment is corrosion of the hydraulic cement by carbonic acid andother corrosive compounds formed by reactions between the carbondioxide, water and potentially other compounds in the environment.Carbonic acid and other corrosive compounds formed from carbon dioxidecan react with and penetrate into hardened hydraulic cement therebylowering the compressive strength thereof. For example, carbonic acidcorrosion can cause the production casing of an oil and gas well to failresulting in undesired migration of fluids between the formation andwell bore and other serious problems. Similar problems and adverseconsequences can occur in other applications in which hydraulic cementcompositions are used in carbon dioxide environments.

There is a need for a hydraulic cement composition that is resistant tocorrosion by carbonic acid in downhole and other environments and thatcan be used in effective and efficient manners.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating one embodimentof the inventive method of enhancing the recovery of a hydrocarbon froma subterranean formation.

FIG. 2 is a graph corresponding to Example 1.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the invention provides a carbon dioxide-resistanthydraulic cement composition. The inventive carbon dioxide-resistanthydraulic cement composition comprises a Portland cement, Class C flyash and water. The Class C fly ash is present in the composition in anamount in the range of from about 5% to less than about 30% by weightbased on the total weight of the cementitious components in thecomposition. The water is present in the composition in an amountsufficient to form a slurry.

In another aspect, the invention provides a method of cementing in acarbon dioxide environment. The inventive method of cementing in acarbon dioxide environment comprises the steps of preparing a carbondioxide-resistant hydraulic cement composition, placing the carbondioxide-resistant hydraulic cement composition in the carbon dioxideenvironment, and allowing the carbon dioxide-resistant hydraulic cementcomposition to set.

The carbon dioxide-resistant hydraulic cement composition utilized inthe inventive method of cementing in a carbon dioxide environmentincludes a Portland cement, Class C fly ash, and water. The Class C flyash is present in the composition in an amount in the range of fromabout 5% to less than about 30% by weight based on the total weight ofthe cementitious components in the composition. The water is present inthe composition in an amount sufficient to form a slurry.

In yet another aspect, the invention provides a method of enhancing therecovery of a hydrocarbon from a subterranean formation. The inventivemethod of enhancing the recovery of a hydrocarbon from a subterraneanformation comprises the steps of: (a) placing one or more injectionwells into the subterranean formation, the injection well(s) including acasing cemented into place using a hydraulic cement composition; (b)placing one or more production wells into the subterranean formation,the production well(s) including a casing cemented into place using ahydraulic cement composition; and (c) injecting a flooding compositionincluding carbon dioxide and water through one or more of the injectionwells into the subterranean formation in order to pressurize thesubterranean formation and drive the hydrocarbon toward the productionwell(s).

The hydraulic cement composition utilized to cement the casing intoplace in at least one of the injection well(s) and production well(s) isa carbon dioxide corrosion-resistant hydraulic cement composition. Thecarbon dioxide corrosion-resistant hydraulic cement composition includesa Portland cement, Class C fly ash and water. The Class C fly ash ispresent in the composition in an amount in the range of from about 5% toless than about 30% by weight based on the total weight of thecementitious components of the composition. The water is present in thecomposition in an amount sufficient to form a slurry.

DETAILED DESCRIPTION

The invention includes a carbon dioxide-resistant hydraulic cementcomposition, a method of cementing in a carbon dioxide environment (the“inventive cementing method”), and a method of enhancing the recovery ofa hydrocarbon fluid from a subterranean formation (the “inventiverecovery enhancing method”). The inventive carbon dioxide-resistanthydraulic cement composition is utilized in both the inventive cementingmethod and the inventive recovery enhancing method.

As used herein and in the appended claims, a carbon dioxide environmentmeans an environment that contains or may contain an amount of carbondioxide capable of causing corrosion to hydraulic cement. For example, acarbon dioxide environment can be an environment that already includescarbon dioxide and water (for example, a subterranean area that containscarbon dioxide and water, and in which a carbon storage capsule isplaced) or an environment that may be subjected to or otherwise includecarbon dioxide and water in the future (for example, a subterraneanformation in which carbon dioxide and water are subsequently injected inconnection with an enhanced oil recovery operation).

The inventive carbon dioxide-resistant hydraulic cement compositioncomprises a Portland cement, Class C fly ash and water. The water ispresent in the composition in an amount sufficient to form a slurry.

The Portland cement utilized in the inventive composition is preferablyselected from Class G type Portland cement and Class H type Portlandcement as classified according to API Specification for Materials andTesting (API Specification 10A), published by The American PetroleumInstitute (hereinafter “API Class G (or API Class H) type Portlandcement”) . More preferably, the Portland cement utilized in theinventive composition is API Class H type Portland cement.

Fly ash is very fine ash produced by the combustion of powdered coal.The Class C fly ash utilized in the inventive composition is Class C flyash as defined in ASTM Specification C 618. Class C fly ash haspozzolanic and cementitious properties. The Class C fly ash is presentin the composition in an amount in the range of from about 5% to lessthan about 30% by weight, preferably in the range of from about 15% toabout 28% by weight, and most preferably about 25% by weight, based onthe total weight of the cementitious components in the composition. Asused herein and in the appended claims, a cementitious component is acomponent that has the properties of hydraulic cement in that itchemically combines with other ingredients to form a hydrated cement. Asused herein and in the appended claims, the expressed percents by weightof the Class C fly ash and Portland cement are based on a dry weightbasis.

In one embodiment, the cementitious components utilized in the inventivecomposition are Portland cement and Class C fly ash. Accordingly, inthis embodiment, the Class C fly ash is present in the composition in anamount in the range of from about 5% to less than about 30% by weight,preferably in the range of from about 15% to about 28% by weight, andmost preferably about 25% by weight, based on the total weight of thePortland cement and the Class C fly ash present in the composition.

Additional components can optionally be included in the inventivecomposition depending on the application. For example, in oneembodiment, a fluid loss additive is included in the composition. Anexample of a suitable fluid loss additive is Halad -344, a fluid lossadditive marketed by Halliburton Energy Services, Inc. and comprising arandom copolymer of 2-acrylamide-2-propane sulfonic acid andN,N-dimethyl acrylamide. A defoamer can also be used in the inventivecomposition. An example of a suitable de-foaming agent is D-AIR 3000L™,a defoamer marketed by Halliburton Energy Services, Inc. and comprisingan internal olefin (C₁₄-C₁₈), an alkaline hydrophobic precipitatedsilica, and polypropylene glycol 4000. Other components that can beutilized in the inventive composition include retarding agents,accelerating agents, silica, elastomers, fibers, hollow beads andfoaming agents. The particular additives and the amount of suchadditives utilized will depend on the particular application.

The components of the inventive composition are admixed together to forma pumpable slurry. The density of the slurry can vary depending on theapplication. Generally, the density of the slurry is in the range offrom about 12 to about 19 pounds per gallon of water in the slurry. Theslurry ultimately hardens and sets into a carbon dioxidecorrosion-resistant hydraulic cement.

The inventive cementing method comprises the steps of preparing a carbondioxide-resistant hydraulic cement composition, placing the carbondioxide-resistant hydraulic cement composition in the carbon dioxideenvironment, and allowing the carbon dioxide-resistant hydraulic cementcomposition to set. The carbon dioxide-resistant hydraulic cementcomposition utilized in the inventive cementing method is the inventivecarbon dioxide-resistant hydraulic cement composition.

The inventive cementing method can be used in connection with anycementing application involving a carbon dioxide environment. Examplesinclude cementing applications involving wells (for example, oil, gas,water, and geothermal wells) penetrating subterranean formations,including primary cementing applications, formations sealing andconsolidation applications, formation of cement plugs for variouspurposes, and remedial cementing applications. Other cementingapplications involving a carbon dioxide environment and in which theinventive cementing method can be utilized include the formation ofunderground cement capsules for storing carbon from power plants andcementing applications used in connection with in situ combustiontechniques used in connection with coal gasification.

The inventive recovery enhancing method can be utilized to enhance theproduction of a hydrocarbon (such as crude oil and/or natural gas) frompartially depleted reservoirs thereof. The inventive recovery enhancingmethod comprises the steps of: (a) placing one or more injection wellsinto the subterranean formation, the injection well(s) including acasing cemented into place using a hydraulic cement composition; (b)placing one or more production wells into the subterranean formation,the production well(s) including a casing cemented into place using ahydraulic cement composition; and (c) injecting a flooding compositionincluding carbon dioxide and water through one or more of the injectionwells into the subterranean formation in order to pressurize thesubterranean formation and drive the hydrocarbon toward the productionwell(s). The hydrocarbon and typically water are then produced throughthe production well(s).

The production well(s) and injection well(s) can be placed into thesubterranean formation by drilling and completion techniques known inthe art. Typically, a plurality of injection wells and production wellsare placed in an oil field (which can include several acres) adjacent tothe subterranean formation(s) of interest. The injection and productionwells are strategically positioned and spaced apart in the oil field toeffectively and efficiently utilize the pressure created by flooding theformation to drive the hydrocarbon from the injection well(s) toward theproduction well(s).

The hydraulic cement composition utilized in the inventive recoveryenhancing method to cement the casing into place in at least one of theproduction well(s) and injection well(s) is the inventive carbon dioxidecorrosion-resistant hydraulic cement composition. The inventivecomposition is preferably utilized to cement the casing into place inall of the production wells and injection wells utilized in theinventive recovery enhancing method. Ideally, the inventive compositionis used in connection with all of the cementing applications carried outin association with the inventive recovery enhancing method.

In cementing the casing into place, the inventive cement composition istypically pumped through the tubular casing and forced into the annularspace between the outside of the casing and the wall of the wellbore.The inventive composition then hardens and sets to bond the casing inthe wellbore and effectively seal the casing from the formation andcarbonic acid and other corrosive fluids that may be present therein.

After the inventive cement composition is set, one or more perforationsare formed in the casing and hardened cement to allow fluids to flowbetween the injection and production wells and the formation. Forexample, components used to flood the formation can be injected throughperforation(s) in the injection well(s) into the formation.Hydrocarbons, water and other fluids can be forced from the formationthrough the perforation(s) into the production well(s).

Methods of enhancing the recovery of a hydrocarbon fluid from asubterranean formation by injecting a flooding composition includingcarbon dioxide and water through one or more injection wells into thesubterranean formation in order to pressurize the formation and drive ahydrocarbon (for example, crude oil and/or natural gas) toward one ormore production wells are well known. The flooding composition can beinjected through the injection well(s) by alternating the injection ofwater and carbon dioxide (water alternating gas (WAG) techniques) or bysimultaneously injecting water and carbon dioxide (simultaneous waterand gas injection (SWAG) techniques).

Flooding the formation with carbon dioxide and water exposes the cementutilized to seal the casings of the production well(s) and injectionwell(s) into place and in connection with other applications associatedwith the wells to carbonic acid and possibly other corrosive compounds.For example, carbonic acid, H₂CO₃, readily forms by reaction of carbondioxide and water. Other potentially corrosive compounds can be formedby reactions between the carbon dioxide or carbonic acid with othercompounds in the formation.

Referring now to FIG. 1, an embodiment of the inventive method ofenhancing the recovery of a hydrocarbon fluid from a subterraneanformation is illustrated. FIG. 1 schematically designates a subterraneanformation 12 that contains a hydrocarbon (in this case a crude oil)deposit therein.

First, an injection well 10 is placed in the subterranean formation 12by drilling a wellbore 16 therein. A metal tubular casing 18 is placedinto the wellbore 16 and cemented into place therein with the inventivecarbon dioxide corrosion-resistant hydraulic cement composition 20.After the cement composition has set, perforations 22 are formed in thecasing 18 and hardened cement composition 20 in the area of thesubterranean formation 12 to allow the injection well 10 to fluidlycommunicate with the formation.

A production well 30 is also placed in the subterranean formation 12 bydrilling a wellbore 32 therein. A metal tubular casing 34 is placed intothe wellbore 32 and cemented into place therein with the inventivecarbon dioxide corrosion-resistant hydraulic cement composition 20.After the cement composition has set, perforations 36 are formed in thecasing 34 and hardened cement composition 20 in the area of thesubterranean formation 12 to allow the production well 30 to fluidlycommunicate with the formation.

Next, carbon dioxide and water are injected into the subterraneanformation 12 through the injection well 10. The carbon dioxide and waterforms a flooding composition 40 in the subterranean formation 12 thatfunctions to pressurize the formation and drive the hydrocarbons (crudeoil in this case) present therein toward and into the production well30. The oil and water are then produced from the production well 30. Dueto the fact that the cement utilized to cement the casings of theproduction and injection wells into place is the inventive composition,the cement effectively resists corrosion by the carbon dioxide injectedinto the formation and related compounds formed thereby.

Many advantages are achieved by the inventive compositions and methods.For example, the inventive carbon dioxide-resistant hydraulic cementcomposition is very effective in resisting corrosion by highconcentrations of carbon dioxide in water under harsh temperature andpressure conditions even though it includes a relatively low amount ofClass C fly ash (when compared to certain prior carbon dioxide-resistanthydraulic cement compositions). In fact, in accordance with theinvention, it has been discovered that a relatively low amount of ClassC fly ash (when compared to certain prior carbon dioxide-resistanthydraulic cement compositions) actually provides better resistance tocarbonic acid penetration into set hydraulic cement compositions. Theinventive composition is very effective in connection with the hightemperatures, high pressures and other harsh conditions that aretypically associated with downhole environments.

The present invention is exemplified by the following example, which isgiven by way of example only and should not be taken as limiting of thepresent invention in any way.

Example 1

The inventive carbon dioxide-resistant hydraulic cement composition wastested in the laboratory for its ability to form hardened hydrauliccement capable of withstanding corrosion by carbon dioxide.Specifically, the effect of varying the amount of the Class C fly ashutilized in the composition on the carbon dioxide corrosion resistanceof the hardened cement samples was evaluated.

Each cement slurry was tested according to API Specification 10, Section5. First, various hydraulic cement composition slurries including theinventive carbon dioxide-resistant hydraulic cement composition wereprepared by admixing Class H Portland cement, Class C fly ash (except informulation No. 1, the control sample), a fluid loss additive(Halad-344), a defoamer (D-Air 3000 L) and distilled water together toform a slurry. The components and density of the slurries are shown byTable 1 below.

TABLE 1 Hydraulic Cement Slurry Formulations Sample Sample Sample SampleFormulation No. 1 No. 2 No. 3 No. 4 Portland cement¹  100%   75%   65%  50% Class C fly ash² 0   25%   35%   50% Halade-344³ 0.25% 0.25% 0.25%0.25% D-AIR 3000L ™⁴ 0.05 g/sk 0.05 g/sk 0.05 g/sk 0.05 g/sk Water⁵  39%   36% 34.5% 32.6% Density⁶ 16.4 ppg 16.4 ppg 16.4 ppg 16.4 ppg¹API Class H type Portland cement. The percent by weight is based on thetotal weight of the Portland cement and Class C fly ash (based on a dryweight basis). ²Class C fly ash as defined in ASTM Specification C 618.The percent by weight is based on the total weight of the Portlandcement and Class C fly ash (based on a dry weight basis). ³A fluid lossadditive sold by Halliburton Company and comprising a random copolymerof 2-acrylamide-2-propane sulfonic acid and N,N-dimethyl acrylamide. Thelisted percent is the percent by weight based on the total weight of thecomposition (based on a dry weight basis). ⁴A defoamer marketed byHalliburton Company and comprising an internal olefin (C₁₄-C₁₈), analkaline hydrophobic precipitated silica, and polypropylene glycol 4000.The recited measurement is in terms of grams per sack of cement.⁵Distilled water. The listed percent is the percent by weight based onthe total weight of the Portland cement and Class C fly ash (based on adry weight basis). ⁶Pounds per gallon

Cylindrical cement core samples of each slurry formulation (No. 1-No. 4)were then formed. Each core sample was 1½ inches in diameter and 2½ longand formed by injecting the corresponding slurry into a plastic mold andallowing the slurry to harden therein. Each slurry was slowly pouredinto the mold and stirred therein to remove any trapped air. The plasticmolds were then sealed with rubber stoppers and the samples were curedin the molds for 15 days at a temperature of 200° F. and a pressure of2000 psi.

Following the curing period, the core samples were removed from themolds by placing the molds in warm water to expand the plastic andpushing the cores therefrom. Utilizing the above procedure, two cementcores were formed for each formulation (No. 1-No. 4).

A first set of the cores (including one of each formulation (No. 1-No.4)) was placed into a first autoclave. A second set of cores (includingone of each formulation (No. 1-No. 4)) was placed in the secondautoclave. The samples were then carbonated for 15 days in autoclave No.1 and 30 days in autoclave No. 2 as follows: The chamber of eachautoclave was filled with water and sealed. Liquid carbon dioxide wasthen continuously injected into the water in each chamber throughout thetest periods using a sparge tube connected to a carbon dioxide tank. Thechambers of the autoclaves were maintained at 200° F. The liquid carbondioxide was injected into each chamber at a pressure of 2000 psithroughout the test periods.

Following each test period (15 days for autoclave No. 1; 30 days forautoclave No. 2), the cement core samples were removed and analyzed forcarbon dioxide penetration depth therein. The depth of carbon dioxide(carbonic acid) penetration into the core samples was determined asfollows: First, each cement core sample was cut in half along itslongitudinal axis. Each core sample was then submerged in a 1%phenolphthalein solution. The phenolphthalein solution turned a portionof each core sample to the color purple which designated the portion ofthe sample that included calcium hydroxide; that is, the portion thathad not reacted with carbon dioxide (carbonic acid). By measuring thethickness of the gray portion of the sample, the carbon dioxide(carbonic acid) penetration depth could be determined. The depth of thecarbon dioxide (carbonic acid) penetration in the core samples wasrepresentative of the resistance (or lack of resistance) of the coresamples to corrosion by carbon dioxide (carbonic acid) under conditionssimilar to the conditions encountered in downhole environments.

The results of the tests are shown illustrated by FIG. 2 and shown byTable 2 below.

TABLE 2 CO₂ Penetration Depth Following 15 and 30 Days of Treatment 15Days 30 Days Percent Class C Penetration Penetration Fly Ash¹ DepthDepth  0%   4 mm   6 mm 25% 0.25 mm 0.25 mm 35%   1 mm   1 mm 50%   2 mm 3.5 mm ¹Class C fly ash as defined in ASTM Specification C 618. Thepercent by weight is based on the total weight of the Portland cementand Class C fly ash (based on a dry weight basis).

The above results show that the Class C fly ash significantly improvedthe resistance of the cement core samples to penetration (and corrosion)by carbon dioxide (carbonic acid). The results also show, surprisingly,that the degree of penetration (and corresponding degree of corrosion)by carbon dioxide (carbonic acid) decreased as the amount of Class C flyash in the composition decreased. For example, the carbon dioxide(carbonic acid) penetration depth in the samples utilizing 25% by weightClass C fly ash (0.25 mm) was significantly less than the carbon dioxide(carbonic acid) penetration depth in the core samples formed using 35%by weight Class C fly ash.

Thus, the present invention is well adapted to carry out the objects andattain the ends and advantages mentioned as well as those which areinherent therein.

What is claimed is:
 1. A carbon dioxide-resistant hydraulic cementcomposition, comprising: a Portland cement; Class C fly ash present inan amount in the range of from about 5% to less than about 30% by weightbased on the total weight of the cementitious components in saidcomposition; and water present in an amount sufficient to form a slurry.2. The carbon dioxide-resistant hydraulic cement composition of claim 1,wherein said Portland cement is selected from API Class G type Portlandcement and API Class H type Portland cement.
 3. The carbondioxide-resistant hydraulic cement composition of claim 2, wherein saidPortland cement is API Class H type Portland cement.
 4. The carbondioxide-resistant hydraulic cement composition of claim 1, furthercomprising a fluid loss additive.
 5. The carbon dioxide-resistanthydraulic cement composition of claim 1, further comprising a defoamer.6. The carbon dioxide-resistant hydraulic cement composition of claim 1,wherein said Class C fly ash is present in said composition in an amountin the range of from about 15% to about 28% by weight based on the totalweight of the cementitious components in said composition.
 7. The carbondioxide-resistant hydraulic cement composition of claim 6, wherein saidClass C fly ash is present in said composition in an amount of about 25%by weight based on the total weight of the cementitious components insaid composition.
 8. The carbon dioxide-resistant hydraulic cementcomposition of claim 1, wherein said Class C fly ash is present in saidcomposition in an amount of from about 5% to less than about 30% byweight based on the total weight of said Portland cement and Class C flyash in said composition.
 9. The carbon dioxide-resistant hydrauliccement composition of claim 1, wherein said composition has a cementdensity in the range of from about 12 to about 19 pounds of cementitiouscomponents per gallon of water in said slurry.
 10. The carbondioxide-resistant hydraulic cement composition of claim 1, wherein aftersaid composition has set, said composition has a cement penetration of 1mm or less after 15 days of carbon dioxide exposure.
 11. The carbondioxide-resistant hydraulic cement composition of claim 1, wherein aftersaid composition has set, said composition has a cement penetration of 1mm or less at 30 days.
 12. A carbon dioxide-resistant hydraulic cementcomposition, comprising: a Portland cement; Class C fly ash present inan amount in the range of from 5% to less than 30% by weight based onthe total weight of the cementitious components in said composition; andwater present in an amount sufficient to form a slurry.
 13. The carbondioxide-resistant hydraulic cement composition of claim 12, wherein saidPortland cement is selected from API Class G type Portland cement andAPI Class H type Portland cement.
 14. The carbon dioxide-resistanthydraulic cement composition of claim 13, wherein said Portland cementis API Class H type Portland cement.
 15. The carbon dioxide-resistanthydraulic cement composition of claim 12, further comprising a fluidloss additive.
 16. The carbon dioxide-resistant hydraulic cementcomposition of claim 12, further comprising a defoamer.
 17. The carbondioxide-resistant hydraulic cement composition of claim 12, wherein saidClass C fly ash is present in said composition in an amount in the rangeof from 15% to 28% by weight based on the total weight of thecementitious components in said composition.
 18. The carbondioxide-resistant hydraulic cement composition of claim 12, wherein saidClass C fly ash is present in said composition in an amount of from 5%to less than 30% by weight based on the total weight of said Portlandcement and Class C fly ash in said composition.
 19. The carbondioxide-resistant hydraulic cement composition of claim 12, wherein saidcomposition has a cement density in the range of from 12 to 19 pounds ofcementitious components per gallon of water in said slurry.
 20. Thecarbon dioxide-resistant hydraulic cement composition of claim 13,wherein said Portland cement is API Class H type Portland cement, andsaid Class C fly ash is present in said composition in an amount in therange of from 15% to 28% by weight based on the total weight of thecementitious components in said composition, said composition furthercomprising: a fluid loss additive; and a defoamer, and wherein aftersaid composition has set, said composition has a cement penetration of 1mm or less at 30 days.